As is known in the art, conventional current sensors can be arranged in either an open loop or a closed loop configuration. An “open loop” current sensor includes a magnetic field transducer in proximity to a current-carrying, or primary, conductor. The magnetic field transducer provides an output signal proportional to the magnetic field generated by current passing through the primary conductor.
A “closed loop” current sensor additionally includes a secondary conductor in proximity to the magnetic field transducer. A current is passed through the secondary conductor in order to generate a magnetic field that opposes and cancels the magnetic field generated by a current passing through the primary conductor. Thus, the magnetic field in the vicinity of the magnetic field transducer is substantially zero. The current passed through the secondary conductor is proportional to the magnetic field in the primary conductor and thus, to the primary current. The closed loop configuration generally provides improved accuracy over the open loop configuration. This is because hysteresis effects associated with the transducer are eliminated by maintaining the magnetic field on the transducer at approximately zero gauss. The closed loop configuration also generally provides improved linearity in comparison with the open loop configuration, as well as increased dynamic range. These improvements are further described below.
Some conventional open and closed loop current sensors contain integrated electronics. For example, an amplifier can be coupled to and provided in an integrated package with the magnetic field transducer. However, in conventional open and closed loop current sensors, the secondary conductor and/or the primary conductor are not integrated with the magnetic field transducer.
One type of conventional current sensor uses a Hall effect transducer as the magnetic field transducer. Typical current sensors of this type include a Hall effect transducer mounted on a dielectric material, for example a circuit board. Typically, a ferrous core is used in proximity to the Hall effect transducer. The secondary conductor and/or the primary conductor are adjacent to, or disposed around, the ferrous core. In part because this conventional closed loop current sensor is relatively large, it suffers from relatively low bandwidth.
Another type of conventional current sensor uses a magnetoresistance element as the magnetic field transducer. The magnetoresistance element changes resistance in response to a magnetic field. A fixed electrical current is directed through the magnetoresistance element, thereby generating a voltage output signal proportional to the magnetic field. When used in an open loop current sensor configuration, the voltage output signal has a magnitude proportional to the magnetic field generated by current passing through the primary conductor. Conventional current sensors of this type use an anisotropic magnetoresistance (AMR) element mounted on a dielectric material, for example a circuit board. The secondary conductor and/or the primary conductor are adjacent to, or disposed on, the dielectric material, for example as circuit board traces. As with the previously described conventional closed loop current sensor, in part because this conventional closed loop current sensor is relatively large, it suffers from relatively low bandwidth.
Various parameters characterize the performance of current sensors, including sensitivity and linearity. Sensitivity is related to a change in the resistance of the magnetoresistance element or the change in output voltage from the Hall effect transducer in response to a change in magnetic field. Linearity is related to the degree to which the resistance of the magnetoresistance element or the output voltage from the Hall effect transducer varies in direct proportion to the magnetic field. Important considerations in the use of both types of magnetic field transducers include the effect of stray or external magnetic fields on the current sensor performance.
Typical current sensors tend to be undesirably large, both in terms of height and circuit board area, due in part to the secondary conductor and/or primary conductor being separate from the magnetic field transducer. Such devices also tend to suffer inaccuracies due, in part, to variation of relative position of the primary conductor, the magnetic field transducer, and the secondary conductor. It would, therefore, be desirable to provide a current sensor having a reduced size and improved accuracy.
While conventional current sensors are described above as having particular disadvantages, it will be appreciated that conventional external magnetic field sensors and also conventional electrical signal isolators suffer from the same disadvantages. It would, therefore, be desirable to provide an external magnetic field sensor and also an electrical signal isolator having reduced size and improved accuracy.